Throughout this patent, position designations such as “above,” “below,” “top” “forward,” “rear,” etc. are referenced to a firearm held in a normal firing position (i.e., pointed away from the shooter in a generally horizontal direction).
Semi-automatic firearms with sensitive cartridge cases, in particular semi-automatic shot guns, have always been problematic. In particular, problems arise due to the extremely low resistance of the cartridges to residual pressure when loading the weapon. With semi-automatic shot guns, it is an additional problem in that cartridges with exactly the same measurements can have very different payloads, which in turn makes for different residual pressures.
Additionally, the breech on many semi-automatic weapons tends to open when the bullet is still in the barrel and/or when the gas pressure has not fallen sufficiently.
With a semi-automatic weapon, like a shot gun or a semi-automatic pistol designed for strong cartridges and/or a long-barreled pistol, low residual pressure will cause most cartridge shells to inflate or burst when the lock is opened. Such residual pressure is unavoidable in a simple semi-automatic pistol with a blow-back breech. But locked recoil operated guns also have residual pressure when the breech opens which some shotgun cartridge shells cannot sustain. Recoil-loading semi-automatic rifles, which are made for weak cartridges, have jamming problems when used with stronger ammunition. These jamming problems can be attributed to the increased residual pressure associated with stronger ammunition.
Some shot-gun cartridge shells have, in the past, been made entirely of metal. However, due to the high price and weight associated with such a construction, such metal shells were not generally accepted.
An additional problem is the low tensile-load capacity of a shot-gun cartridge shell in its longitudinal direction. With cheap shot-gun cartridge shells made of cardboard with metal bottoms, such loads may cause the metal bottom in the cartridge chamber to separate from the remainder of the shell. The low conicity of shot-gun cartridges contributes to this tendency.
For approximately 100 years, shot guns have used a recoil-loading system in which, upon the firing of a shot, the barrel and the closed breech first recoil back over the full recoil range. The pressure is almost completely dissipated in this run-back process. (Browning, Walther type weapons utilize this sort of recoil loading system.) In such systems, after the breech reaches the rearmost position, it remains fixed and the barrel is decelerated under the power of a spring such that the barrel is returned relatively slowly towards the front. The breech and the cartridge shell remain stationary as the barrel returns to the forward position, so that the cartridge is gently extracted from the barrel. Thus, excessive longitudinal forces do not act upon the cartridge shell. After the ejection of the cartridge shell, the breech snaps forward again under the effect of the closing spring. In the process, the breech carries a new cartridge forward into the cartridge chamber.
Such a shot gun is very reliable—even with differently charged ammunition. But, it has two different disadvantages. First, a built-in brake is provided to slow the movement of the barrel and perform an adjustment for extreme cartridge charge differences (i.e., for different sized cartridges). However, this brake only works under strictly defined conditions (for example, only when the components are lightly oiled). Second, the relatively slow, powerful backwards movement of the barrel requires support from the housing. This support takes place in that the weapon is pressed into the shoulder of the shooter. However, if the weapon is shot from the hip, then this support is not provided, which can lead to serious loading malfunctions. Such a system is, therefore, not suitable for shot guns that are used in military and/or police applications.
Recently, the tendency has been to switch to gas pressure loaders for shot guns. Gas pressure loaders have long been used in semi-automatic rifles and have proven themselves in that context. But, semi-automatic shot guns require a defined gas pressure and an easily removable, rugged shot cartridge shell. With modern, powerful cartridges that have a cartridge floor made of metal with a long sleeve and a shell body made of longitudinally ribbed plastic, such gas pressure loader shot guns enjoy trouble-free operation. Moreover, even with poor quality cartridges, gas pressure loader firearms do not have the support disadvantage of recoil-loading shot guns. Thus, the gas pressure loader functions the same when the weapon is fired from the hip and when the weapon is fired from the shoulder.
However, gas pressure loaders are very complicated. Depending on the powder used, they require different levels of cleaning and are susceptible to dirt, rust, and lack of oil due to the many metal-on-metal contact areas. Cutting down on gas pistons by loading the breech with drawn-off powder gases leads to structural simplification, but increases the risk of fouling.
Modern recoil loaders are also known that operate without movement of the barrel (e.g., the G3 weapon). However, this functionality is achieved at a cost in sensitivity with respect to ammunition. In other words, such recoil loading weapons, in particular these types of shot guns, are very sensitive as far as ammunition is concerned.
Another recoil-loading system that is locked, but still has a rigid barrel, is also known for shot guns. This system, which is described in U.S. Pat. No. 4,604,942, has a bolt head carrier seated loosely in the weapon. The bolt head carrier remains in position due to its mass inertia while all other parts of the weapon run backwards due to the recoil. The bolt head carrier and the bolt head are constructed such that they eventually strike each other. This seemingly simple weapon is, in fact, very complicated. Moreover, the recoil loading system does not seem to function safely, as a weapon that came to market with this system is no longer offered for sale.
This system was later combined with a pump gun mechanism in the Benelli Super M 3. In that combination, the semi-automatic activity could be optionally disabled. These known weapons have a tube magazine, which is not practical for a service weapon.
Soon after the emergence of the repeating firearms with cylinder breech mechanisms, attempts were made to simplify the loading motion. To load by hand, the marksman had to make a transverse motion, a back motion, a forward motion and again a transverse motion. Consequently, a kind of worm gear was developed, which converts a simple back and forward motion into the above specified complicated movement. Due to the complicated mechanics, these so-called straight pull action systems either did not prove themselves or were too expensive. In the case of these known straight pull action systems, a breech block is assigned to the actual breech or bolt head, which could be viewed as a bolt head carrier.
There are also other systems for simplifying the loading motion. Such a system was realized prior to the above named straight pull action system. In that earlier system, the breech can be moved in a straight line forward until reaching the cartridge base in the cartridge chamber. When the breech reaches this position, a cross slide or locking block is moved into recesses in the breech and into the case of the weapon to thereby lock the breech. A bottom lever is rotated downward in an arc-shaped motion in an initial run to release the locking block. The unlocked breech is then pulled back in an end run. The breech is not closed and locked until the bottom lever is rotated upward. A box magazine has also been known for use with this system since 1895.
Similar systems are not activated by a bottom lever, but rather by a slide which is joined to the fore end and can be moved in a straight line. However, in these systems, the locking block executes a rotating motion.
All of the above described systems are quite complicated and correspondingly expensive and sensitive.
In the case of locking blocks with bottom levers and fore end loaders, particularly in the case of those that use heavy cartridges, high surface pressures occur. These pressures can only be counteracted by awkwardly shaped constructions or extremely high precision.
Particularly in the case of weapons for emergency use, ruggedness, small dimensions, and reliability should be combined with a low price. Such weapons are typically only used in rare emergencies, but then they must function safely under difficult circumstances.
U.S. Pat. No. 3,906,651 appears to illustrate a cartridge with a round profile seated on the breech block of a breech that has two opposing extractor hooks.